In recent years, liquid crystal display devices have been rapidly spreading instead of conventional CRT displays since the devices have characteristics of electric power saving, light weight, a thin form, and others. The liquid crystal display which constitutes any ordinary liquid crystal display device has a structure in which a liquid crystal layer made of a liquid crystal material having a regular configuration is held between two substrates having alignment layers, and has a function that the configuration state of the liquid crystal material is changed by the application of a voltage to between the substrates so as to display images.
The display quality of images based on liquid crystal displays depends on the configuration state of the liquid crystal material. When the configuration state of the liquid crystal molecules is made even, a good display quality can be obtained. Many factors which produce an effect on such a configuration state of liquid crystal material are known. One of the factors is the gap between the two substrates, between which the liquid crystal layer is held (the cell gap). The cell gap corresponds to the thickness of the liquid crystal layer. In order to obtain an excellent display quality, it is essential to fix the substrates to make the cell gap highly precise and uniform. In particular, recently, an increase in the screen size of liquid crystal display devices has been advancing; thus, there has been caused a problem that the display quality is deteriorated by a matter that the cell gap is fluctuated between the upper of the screen and the lower of the screen by an effect of gravity and others. Such a problem becomes in particular serious in liquid crystal displays using a ferroelectric liquid crystal.
Ferroelectric liquid crystal (FLC) exhibits a very fast response in order of microseconds, and thus FLC is a liquid crystal suitable for high-speed devices. In recent years, attention has been paid to ferroelectric liquid crystal in which the liquid crystal layer thereof is stable in a single state (herein after referred to as “monostable”) when no voltage is applied thereto as a liquid crystal making it possible to attain gray scale display by the matter that the director (the inclination of the molecule axis) of the liquid crystal is continuously changed by a change in applied voltage so as to analogue-modulate the light transmission thereof (Non-Patent Document 1. FIG. 13). As the ferroelectric liquid crystal that can be made into a mono-stability state in the liquid crystal phase, there are a material having the phase change of cholesteric phase (Ch)-chiral smectic C phase (SmC*) without the transition to the smectic A (SmA) phase in the temperature lowering process and a material having the phase change of Ch-SmA-SmC* so as to show the SmC* phase via the SmA phase in the temperature lowering process (FIG. 14).
Ferroelectric liquid crystal has a higher order of molecules therein than nematic liquid crystal; therefore, the former liquid crystal is not easily aligned so that defects called zigzag defects or hairpin defects are easily generated. Such defects cause a fall in contrast based on light leakage. Moreover, the ferroelectric liquid crystal undergoing phase transition via no SmA phase in the phase sequence generates two domains different in the layer normal-line direction thereof (herein after referred to as “double domains”) (FIG. 14). The double domains give such display that black and white are reversed when driven so as to cause a serious problem (FIG. 15). On the other hand, since the ferroelectric liquid crystal having the SmA phase in the phase sequence in general has two stable states for one layer normal so as to show the bi-stability, it is difficult to obtain a mono-stability state. From such a fact, in liquid crystal displays using a ferroelectric liquid crystal, it becomes in particular necessary that the cell gap is not fluctuated in order to stabilize the ferroelectric liquid crystal, the configuration of which is not originally controlled with ease, into a mono-stability state.
The cell gap of liquid crystal displays is usually kept constant by arranging members called spacers between their substrates. The method using such spacers is roughly classified to a method using bead-form spacers, and a method using column-form or wall-form spacers.
The method using bead-form spacers is a method of causing bead-form spacers having an even particle diameter to be present in the liquid crystal layer, thereby controlling the cell gap. The method has an advantage that the cell gap can easily be made even. However, in the bead-form spacer used method, the arrangement locations of the bead-form spacers in the liquid crystal layer cannot be controlled. Thus, the bead-form spacers are unfavorably provided in pixel regions, which are indispensable for the display of images, so as to cause a problem that the display quality of the liquid crystal display falls. Moreover, the bead-form spacer used method is not a method of fixing the two substrates positively; therefore, there is also caused a problem that an advantageous effect is not produced onto external force in the direction along which the cell gap is made wide although a good advantageous effect is produced onto external force in the direction along which the cell gap is made narrow.
On the other hand, the column-form or wall-form spacer used method has an advantage that a fall in the display quality can be prevented since the spacers can be provided by a photolithography method and other methods in regions other than the pixel regions, which are indispensable for the display of images. However, this method is not a method of fixing the two substrates positively, either; therefore, an advantageous effect is not produced onto external force in the direction along which the cell gap is made wide.
In such circumstances, Patent Document 1 discloses a method of using spacers having a photo thermal conversion function, arranging the spacers between two substrates having thermoplastic alignment layers, and then radiating light thereto so that heat is generated in the spacers so as to melt-bond the alignment layers of the two substrates and the spacers, thereby fixing the two substrates with a constant gap. Such a method is useful since the substrates can be strongly fixed with the constant cell gap. However, the constituent material of the alignment layers is limited to thermoplastic materials. Thus, there remains a problem that the scope to which the present method can be applied is narrow.
Patent Document 1: Japanese Patent Application Laid-Open No. 2004-13098
Non-Patent Document 1: NONAKA, T., LI, J. OGAWA, A., HORNUNG, B., SCHMIDT, W., WINGEN, R., and DUBAL, H., 1999, Liq. Cryst., 26, 1599